Acetabular component with improved liner seal and lock

ABSTRACT

An acetabular component for a hip replacement system comprises an acetabular shell, and a liner having a seal for insertion into the acetabular shell. In the preferred embodiment, the shell has a smooth tapered surface in its peripheral inner surface, and the liner has several annular ridges protruding from its outer surface. Upon insertion of the liner into the shell, the annular ridges of the liner come into sealing engagement with the smooth tapered surface of the shell. This sealing engagement substantially prevents a migration of debris along an interface of the liner with the shell. The liner is provided with several peripheral tabs for interference fit with several peripheral notches in the shell. An interlock comprising another liner ridge and a shell groove, provide a positive engagement to hold the liner in the shell as it bottoms therein. In an alternative embodiment, each notch is provided with protruding lips which project into the notch and firmly grasp one of the tabs of the liner upon insertion of the liner into the shell. In this manner, micromotion between the liner and the shell is substantially inhibited.

This application is a continuation of application Ser. No. 08/466,607filed on Jun. 6, 1995 now abandoned.This is a reissue of U.S. Pat. No.5,766,260, issued Jun. 16, 1998, which was based on application Ser. No.08/847,887, filed Apr. 28, 1997, which is a continuation of applicationSer. No. 08/466,607, filed Jun. 6, 1995, abandoned.

BACKGROUND OF THE INVENTION

Prosthesis components for replacing anatomical joints are well known inthe art, including total hip replacement systems. These systems includeacetabular components and femoral components which interact with theacetabular components to replicate the articulation between the head ofa femur and an acetabulum, or cotyloid cavity, of a pelvic girdle. Theacetabular component typically comprises two parts, a metal acetabularshell and a polyethylene liner for insertion into the acetabular shell.

Acetabular shells typically have openings in the shell, including screwholes, which give rise to at least two problems. First, wear debris thatis generated from the articular movement between a femoral headcomponent and the liner can migrate between the liner and the acetabularshell, pass through the openings in the acetabular shell, and causedamage to the bone into which the acetabular shell is implanted. Second,debris can also be generated as a result of minor movement between theliner and the acetabular shell, commonly known as micromotion. Thisdebris can also pass through the openings in the acetabular shell andcause damage to the bone.

Some efforts have been made to address this second problem, includingproviding an acetabular shell with a polished inner shell surface so asto minimize the amount of debris generated. Additionally, severalmanufacturers provide shells and liners with a variety of tongue andgroove like configurations, such as generally rectangular tabs andindentations for mutual engagement. While these interlocking means serveto reduce the amount of debris generated by micromotion, they fail tosolve the problem of migration of debris from the prosthetic articularsurface between the acetabular shell and liner. Thus, despite theseefforts, large numbers of polyethylene particles still have access tothe acetabular bone.

Another approach, which attempts to address both of the debris problemsmentioned above, particularly for acetabular shells having screw holes,is to utilize what are known as “man-hole covers,” or plugs, forinsertion into unused screw holes to prevent the migration of debristherethrough. The main disadvantage of this approach is that the plugsfail to prevent the migration of debris through holes that have bonescrews inserted therethrough. The debris will still migrate around thescrews and through the holes, and ultimately damage the bone.Additionally, many acetabular components are now made without screwholes to prevent migration of polyethylene debris into bone behind themetal shell, but this can compromise fixation of the shell to bone incases in which screws are necessary.

The inventor herein is aware of only one design that obviates both ofthe problems mentioned above, but the usefulness of this design has itsown limitations. The acetabular shell is provided with a tapered innersurface for interfacing with a liner having a corresponding taper.Because the taper interface must fit tightly with each other to beeffective, it is virtually impossible to seat the polyethylene lineronto the inner dome surface of the metal shell. Because the liner onlycontacts the acetabular shell about the peripheral edge of the shell tocreate an annulus of contact, part of the liner, which extends into theacetabular shell, is unsupported. Although such a configuration doesprovide a sealing effect between the liner and the acetabular shell, thedesign is unsuitable as liners formed from polyethylene deform over timewhich interferes with the desired smooth motion between the head andliner. Moreover, because all the load exerted on the liner isconcentrated at the peripheral interface with the acetabular shell, thethickness of the shell must be relatively large, which, for acetabularcomponents of smaller joints, requires a relatively and unacceptablythin liner. If the tapered portions of the shell and liner are madelarge enough to avoid distortion of the polyethylene shell, then thisleaves no room for screws to be placed through the most effectiveportion of the shell's dome.

What is needed is an acetabular component that provides a seal for theinterface of the acetabular shell with the liner, that can substantiallyinhibit micromotion between the acetabular shell and liner, and thatprovides adequate support for the liner across substantially all ofliner so that the liner can be formed from polyethylene.

SUMMARY OF THE INVENTION

The acetabular component for a hip replacement system according to thepresent invention comprises an acetabular shell and liner, with anintegrally formed seal and interlock. The seal is formed between theacetabular shell and the liner upon insertion and interlock of the linerinto the acetabular shell. The seal is provided to substantially preventa migration of poly debris along an interface of the outer surface ofthe liner with an inner surface of the acetabular shell. The interlockprovides a positive engagement between the liner and shell to indicate acomplete and proper seating of the liner and shell. The outer surface ofthe liner is of a shape complementary to the inner surface of theacetabular shell so that substantially all of the outer surface of theliner is supported by the acetabular shell upon insertion of the linerinto the shell.

In the preferred embodiment, the seal is provided as an integral part ofthe liner, and comprises several annular ridges protruding from theouter surface of the liner and having a generally sloped triangularcross-sectional configuration. The acetabular shell is provided with aperipheral, smooth portion in its inner surface and positioned so thatthe seal, or annular ridges, of the liner is in sealing engagement withthe smooth inner surface upon insertion and interlock of the liner intothe acetabular shell. The smooth portions could alternatively be roughor roughened with ripples or ridges, non-tapered, non-cylindrical,non-recessed, or otherwise shaped, oriented, or configured as long asthey provide a sealing surface for the annular ridges. The interlock isalso provided as an integral part of the liner and comprises aninterrupted ridge extending circumferentially between the tabs,described infra. The shell has a matching interrupted groove extendingbetween the notches, described infra. The interlock is engaged as theinterrupted ridge moves into the groove and the liner seats within theshell.

The sealing engagement of the seal ridges with the smooth portionprevents debris generated by the articulation of a femoral headcomponent with the inner surface of the liner from migrating along theliner/shell interface. This ultimately prohibits the debris from passingthrough openings in the acetabular shell and damaging the bone intowhich the acetabular component is implanted. Typically, these openingsin the acetabular shell include screw holes provided for attaching theacetabular shell to the bone with bone screws.

All of the annular ridges and liner are formed from polyethylene, andare therefore resilient. During insertion of the liner into theacetabular shell, he seal ridges will flex as they are forced againstthe inner surface of the acetabular shell, and remain at least partiallyflexed as they are seated into the seal recess. As the interlockengages, the seal ridges will, due to their resiliency, attempt toreturn to their original configuration, and will then be in sealingengagement with the seal recess. Since the ridges are resilient, theyallow the polyethylene liner to seat fully in the dome of the metalshell to achieve full support of the polyethylene.

The liner is provided with several peripheral tabs for interlockingengagement with several notches provided about the periphery of theacetabular shell. The tabs are rounded to facilitate insertion into thenotches and are located to permit bottoming of the insert into the shellbefore they themselves bottom. In a first embodiment, the notchsidewalls are rectangular cut and form an opening slightly smaller thaneach tab to thereby provide an interference fit to control relativerotation. In an alternative embodiment, each notch has two lipsprojecting into the notch opening for firmly grasping a correspondingtab of the liner upon insertion of the liner into the shell. In eitherembodiment, the tabs of the liner must be forced into the notches of theshell, and in this manner, micromotion between the liner and the shellis substantially inhibited.

While the principle advantages and features of the invention have beendescribed above, a greater understanding of the invention may beattained by referring to the drawings and the description of thepreferred embodiment which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the shell of the acetabular component ofthe present invention;

FIG. 2 is a cross-sectional view of the shell taken along the plane ofline 2—2 in FIG. 1 and detailing the shell sealing surface and interlockgroove;

FIG. 3 is a partial view of an alternative embodiment of the shellnotches;

FIG. 4 is an elevational view of a liner of the acetabular component forinsertion into an acetabular shell; and

FIG. 5 is a partial view of the lower periphery of the liner anddetailing the seal and interlock ridges.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The prosthesis component of the present invention is an acetabularcomponent for a hip replacement system. FIG. 1 includes an acetabularshell 32 with a plurality of screw holes 34 and a plurality ofperipheral notches 36. The acetabular shell 32 has an inner surface 38and an outer surface 40. The outer surface 40 is generallyhemispherical, and is contoured to closely match the shape of ahemispherically reamed acetabular, or cotyloid cavity, into which theshell 32 is to be implanted. The inner surface 38 of the shell 32 isalso generally hemispherical, except near its peripheral edge which isrelatively flat, and smooth as best seen in FIG. 2.

The liner 42, as shown in FIGS. 4 and 5, is designed to be inserted intothe acetabular shell 32. The liner has an inner surface 44 thatinterfaces with a femoral head component (not shown) of the hipreplacement system. The liner is constructed from ultra high molecularweight polyethylene or other similar material, and has an outer surface45 machined to a shape complementary to the inner surface 38 of theacetabular shell 32. As a result, substantially all of the hemisphericalouter surface 45 of the liner is in mutual contact with the innersurface 38 of the acetabular shell 32 upon insertion of the liner 42into the shell 32. This congruency between the liner and shell, whilenot necessary to realize the sealing aspects of the present invention,is structurally advantageous as it results in a distribution of forcesfrom the femoral head component to be transmitted to the shell 32through compression of liner 42, thereby allowing the shell 32 to berelatively thin.

As a result of articular movement between the femoral head component andthe inner surface 44 of the liner 42, polyethylene and metal debris isgenerated. Ordinarily, this debris can migrate along the interface ofthe liner 42 and the shell 32, then through any opening in the shell 32,and consequently disease the bone. The congruency between the liner 42and the shell 32, by itself, is insufficient to prevent this debrismigration. For this reason, the liner 42 is provided with a peripheralseal 46 for substantially preventing a migration of debris. The seal 46is positioned so that it forms a barrier for debris traveling betweenthe shell inner surface 38 and the liner outer surface 45, towards theshell holes 34.

As shown in FIGS. 4 and 5, the seal 46 of the preferred embodiment ispartially formed as an integral part of the liner 42. The seal 46includes one or more annular ridges (two are shown) 48 and 50 whichprotrude from a peripheral, slightly-tapered surface 52 of the liner 42.Although two ridges 48, 50 are shown, it is contemplated that othernumbers of ridges would also work effectively. As shown in FIG. 5, theannular ridges 48, 50 have a generally sloped configuration to easeinsertion into the shell 32, although other configurations can beutilized with similar effect. With the sloped configuration shown, theridges 48, 50 are readily flexed upon insertion of the liner 42 into theshell 32. The seal ridges 48, 50 are also formed from ultra highmolecular weight polyethylene, and are therefore relatively resilient.Although the ridges 48, 50 have been described as being an integral partof the liner 42, the seal 46 could alternatively be provided as aseparate component, or as an integral part of the shell 32.Additionally, other sealing configurations can also be used, and theseal 46 can be constructed from other suitable sealing materials aswould be obvious to those skilled in the art.

Although the sealing surface of the shell is depicted smooth andtapered, it could also be rippled or have small ridges and still allowthe flexible sealing ridge to achieve a tight seal. It could also becylindrical with parallel walls and still allow sealing. The acetabularshell 32 of the preferred embodiment includes a matching slightly smoothtapered surface 53 formed along its peripheral inner surface which, asshown in FIG. 2, is positioned to receive the annular ridges 48, 50 withthe ridges 48, 50 and the smooth tapered surface 53 in sealingengagement upon insertion of the liner 42 into the shell 32. The sealingengagement of the annular ridges 48, 50 with the annular sloped surface53, upon insertion of the liner 42 into the acetabular shell 32,substantially prevents the migration of debris along the liner and shellinterface.

In addition to the seal 46, the liner 42 “snap” fits and interlocks intoshell 32 through an interlocking ridge and groove. As shown in FIG. 2,the smooth tapered surface 53 is “grooved” with an interlock groove 54which receives an interrupted interlock ridge 56 which extends aroundthe peripheral circumferential edge of liner 42. As liner 42 is insertedinto shell 32 and “bottoms” out therein as desired, interlock ridge 56“snaps” into interlock groove 54 to positively retain liner 42 withinshell 32. This ensures that liner 42 mounts securely within and“bottoms” in shell 32 as desired, and also provides an indication to thesurgeon that the liner 42 has bene correctly and properly secured withinshell 32. As with seal 46, the location of interlock groove 54 andinterlock ridge 56 may be reversed, provided separately, or otherwiseassembled with liner 42 and shell 32, and interlock ridge 56 need not beinterrupted.

The shell screw holes 34 are utilized to secure the shell 32 to theacetabulum into which the shell 32 is implanted. Ordinarily, bone screwsare inserted through one or more of screw holes 34 from inside the shell32, and are then screwed into the bone contacting the outer surface 40of the shell 32. Alternatively, modular pegs can be used instead of bonescrews, or the shell 32 can be cemented or press fitted into anacetabulum, or some combination of these means for attaching. Althoughthe shell 32 of the preferred embodiment is metallic, non-metallicmaterials could also be used in the construction of the shell.

While the shapes of the matching surfaces of the acetabular shell 32 andliner 42 have been described and shown as generally hemispherical, othershapes could be utilized in a particular application. As shown in thedrawings, the surfaces are customarily machined to close tolerance toachieve an accurate conformance. It is desirable for the liner innersurface 44 to be generally hemispherical to accommodate rotationalmotion with a femoral component to simulate the articulation between ahead of a femur and an acetabulum. Furthermore, while the acetabularcomponent of the preferred embodiment utilizes only one seal 46 and oneinterlock, the acetabular shell can have more than one such seal, witheach seal surface having one or more corresponding seal ridges 48 and 50on the liner 42, without departing from the scope of the presentinvention. Alternatively, the seal 46 could be located more closely tothe screw holes 34, and even surround them separately or protrude intothem.

In the preferred embodiment, the liner 42 is provided with one or moreperipheral tabs 60 for engagement with several peripheral notches 36 inthe shell 32 upon insertion of the liner 42 into the shell 32. Forconvenience in manufacture, peripheral notches 36 may be generallyrectangular. The tabs 60 are sized to be slightly wider than each ofnotches 36 in order to provide an interference fit therebetween andthereby rotationally locate the liner 42 within shell 32. The uppersurface of tabs 60 is generally sloped or rounded on either side tofacilitate insertion of liner 42 and tabs 60 into shell 32 and notches36, respectively. As explained above, as the liner outer surface 45“bottoms” in the shell's inner surface 38, interlock ridge 56 engagesinterlock groove 54 which ensures that tabs 60 are sufficiently insertedinto notches 36 so as to achieve an interference fit and reducemicromotion. As shown in FIGS. 1 and 4, in the preferred embodiment, sixtabs 60 surround the circumference of liner 42 while twelve notches 36surround the circumference of shell 32. The inventor has found that sixtabs 60 are sufficient and adequate to securely position liner 42 withinshell 32 while the additional notches 36 provide greater flexibility inalignment of the liner 42 with respect to the shell 32.

To further prevent micromotion between the liner 42 and the shell 32,each notch 36 may be provided with protruding lips 78, 80 as shown inthe alternative construction in FIG. 3. These lips 78, 80 project intothe notches 36 and firmly grasp the tabs upon insertion of the liner 42into the shell 32. In this manner, relative motion, or micromotion,between the liner 42 and the shell 32 is further substantiallyinhibited. Alternatively, the tabs 60 of the liner 42 could be lipped,and the notches 36 could have tapered sides, or the shell 32 could beprovided with tabs 60 and the liner 42 provided with notches 36, witheither the tabs 60 or the notches 36 being lipped, possibly inconjunction with tapered sides of the non-lipped member for ease ofinsertion.

While the liner 42 has been described as being formed from polyethylene,liners comprising other types of materials can also be used with thepresent invention where similar problems with debris generation ormigration exist, or where sealing between the liner 42 and shell 32 isotherwise necessary.

To implant the acetabular components of the present invention, anappropriately sized component must be selected with consideration ofanatomical and biomedical factors such as the patient's age, activitylevels, weight, and bone and muscle conditions. Preparation of theacetabular cavity is necessary prior to insertion of the component.Thereafter, the acetabular shell can be inserted into the cavity andattached by any of the means described above. Where bone screws ormodular pegs are to be utilized, the acetabular shell must be affixedprior to inserting the liner into the shell. Inserting the liner intothe shell typically requires impacting the liner, which will cause theannular seal ridges to flex. The interlock ridge must also be forcedpast the outer lip of the shell and into the interlock groove whichseats the liner in the shell, the seal, and the tabs into the notches.At that time, the annular seal ridges, due to their resiliency, will bein sealing engagement with the annular seal surface, therebysubstantially preventing a migration of debris between the liner andshell. Meanwhile, the tabs of the liner have an interference fit intothe notches, with the lips of each notch firmly grasping its respectivetab (alternative embodiment), thereby substantially inhibitingmicromotion between the liner and the shell.

While the prosthesis component of the present invention has beendescribed as an acetabular component for a hip replacement system, thisdescription is not intended to be limiting. The prosthesis component ofthe present invention can be utilized in other articulating anatomicaljoint systems, such as shoulder joint systems, and not limited to balland socket joints, and is equally suited for other types of uses,including veterinarian applications.

There are various changes and modifications which may be made to theinvention as would be apparent to those skilled in the art. However,these changes or modifications are included in the teaching of thedisclosure, and it is intended that the invention be limited only by thescope of the claims appended hereto.

1. An acetabular component comprising: an acetabular shell, said shellincluding at least one screw hole formed therein, said shell including asmooth inner sealing surface; said acetabular shell also having at leastone interlock circumferential groove and a plurality of peripheralnotches formed therein; a liner configured to seat within saidacetabular shell, said liner including at least one circumferentialperipheral annular seal, said at least one peripheral seal engaging saidsmooth inner sealing surface of said acetabular shell in a sealingengagement to restrict migration of debris toward said at least onescrew hole; said liner also including a separate raised locking ridgepositioned to engage said interlock groove of said acetabular shell in asnap-lock arrangement; and a plurality of generally rounded peripheraltabs on the peripheral edge of said liner, said tabs disposed to engagesaid plurality of notches on said acetibular shell so as to preventrotational movement of said liner within said acetabular shell.
 2. Theacetabular component of claim 1 wherein said acetabular component isload bearing, said liner being formed to substantially conform to andcontact said shell under load bearing conditions, said at least oneperipheral seal being positioned to maintain its sealing engagementbetween said liner and smooth inner sealing surface of said shell underload bearing conditions.
 3. The acetabular component of claim 2 whereinsaid at least one seal includes at least one ridge of resilient materialso that load bearing contact between said liner and said shell maintainssaid ridge a sealing engagement therebetween.
 4. The acetabularcomponent of claim 3 wherein each of said at least one ridges is anannulus integrally formed on said liner, and said smooth inner sealingsurface is sized and spaced to receive and seat all of said at least oneridges, said seal thereby restricting migration of debris.
 5. Theacetabular component of claim 4 wherein said at least one seal extendsannularly around the liner to thereby restrict debris from passing tothe screw holes.
 6. The acetabular component of claim 1 wherein eachnotch includes a pair of inwardly projecting lips to grasp said tabs asthey engage.
 7. A prosthesis comprising: a shell having at least onescrew hole formed therein and a smooth inner sealing surface; a linerconfigured to seat within said smooth inner surface of said shell, saidliner including at least one circumferential peripheral annular sealflexibly and sealingly engaging said smooth inner sealing surface ofsaid shell to restrict migration of debris toward said at least onescrew hole; said shell having a plurality of peripheral notches therein;and said liner having a plurality of tabs extending outwardly from theliner with each tab being received in a respective one of said notchesin said shell, each said notch having a pair of inwardly projecting lipsto grasp its respective said tab.
 8. The prosthesis of claim 7, whereinwith said tabs so disposed in said notches, micromotion of said linerwithin said shell is inhibited.
 9. A component for an orthopedic jointreplacement system, said component comprising a metal shell adapted tobe affixed to a bony structure within the human body by means of bonescrews, said shell having one or more holes therein for reception ofsaid bone screws and an inner surface, a liner of a suitable syntheticresin material adapted to fit closely within said inner surface of saidshell, said liner constituting a bearing surface for another componentof said joint replacement system, said liner having at least oneflexible seal extending outwardly from said liner for sealing engagementwith said inner surface of said shell around the entire liner so as toprevent the migration of joint fluid and debris from said joint to saidscrew holes, said seal being configured so as to flex upon insertion ofsaid liner into said shell after said shell has been affixed to saidbony structure by said bone screws, said liner further having a lockseparate from said seal, said lock comprising a plurality of notches inan upper peripheral edge of said shell and a plurality of tabs, at leastone notch for each said tab, said tabs extending outwardly from saidliner and being adapted to be received in said notches upon installationof said liner into said shell, each said notch having a pair of inwardlysloping sidewalls cooperating with said tabs so as to substantiallyinhibit micro motion between said liner and said shell.
 10. Theprosthesis of claim 7, wherein each of said tabs has a rounded surfaceand an flat surface, wherein said rounded surfaces bear on the base ofsaid recess and wherein said lips engage said flat surface of said tabsas the tabs are received within said notches.